The present invention is directed to an improvement of the swing-motion truck disclosed in U.S. Pat. No. 3,670,660-Weber, et al. The conventional swing-motion truck disclosed in the above-identified patent has proven extremely successful and has provided a degree of operating efficiencies not previously achieved. The conventional swing-motion truck was designed to lower the critical speeds at which periodic track disturbances could cause resonance conditions with the sprung car body, and, therefore, uncontrolled car body hunting. At low critical speeds, resonance can be effectively controlled by the damping mechanism of the truck, avoiding uncontrolled hunting. The hunting phenomenon causes excessive wear on the wheel flanges and the ultimate problem of derailing and toppling of the car itself. The swing-motion truck disclosed in said patent decouples the lateral movement and forces of the axle and truck side frames from the truck bolster and the car body, thereby substantially isolating the transverse or lateral forces impinging on the wheels and side frames, arising either from rail irregularities or the hunting phenomenon itself, such swing-motion truck providing a dual range of lateral suspension stiffness or rigidity, as completely set forth in said patent. One of the important features of the conventional swing-motion truck is the unique support and load transfer of the car body and lading via its center plate and the transverse truck bolster to the side frames of the truck. This was achieved by a transverse platform or transom spanning laterally across the width of the truck, each end of the transom being supported on a respective rocker seat and held in alignment via a plurality of upstanding bosses received in apertures formed in the ends of the transom proper. The rocker seats allow for the relative transverse swinging of the respective side frames to achieve the decoupling of the transverse lateral forces of the truck from impacting directly upon the truck bolster and the car body, the rocker seats also providing a limit stop in either angular direction to the movement of the respective side frame, which, in the preferred embodiment disclosed therein, is three degrees in either direction, which allows for lateral translation of the bolster in either direction of approximately 5/8 of an inch. Such limit stops define the end of the first stage of resistance to the lateral movement of the side frames, thereafter the second stage coming into play, which second stage provides a considerably greater resistance, which is achieved by the opposition to the lateral movement of the bolster via the lateral deflections of the load spring groups, which resiliently support the ends of the truck bolster and, therefore, the car body. The degree of resistance to lozenging movement of the side frames and axles relative to the truck bolster is also directly dependent upon the weight of the car body, and whether it is in its loaded or unloaded state. This is directly attributable to the fact that the transverse connecting transom is interconnected with the rocker seats via the above-described apertures and upstanding bosses, so that the rigidity against lozenging of the truck itself, including the two axle sets thereof, the pair of swing-mounted side frames thereof, as well as the pair of side-frame rocker seats, is directly affected by the weight of the car body itself, as well as the load thereof, since the interconnection between the two opposite side frames of the truck proper is via the pair of rocker seats and the transverse transom, which interconnect via the frictional contact therebetween. Additional problems arise in the rigidity of the truck during wear and tear of the truck proper, in that the upstanding bosses received within the apertures of the transom allow for a certain amount of play or relative pivotal movement between transom and rocker seat, which play, over time, increases the greater the wear and tear, further compromising the rigidity of the truck structure, and tending to increase the amount of lozenging of the truck elements, or parallelogramming. The total resistance to lozenging of the truck is dependent upon a few factors, such as the resistance of the friction wedges cooperating with the inclined rear surfaces and vertical side walls of the bolster wedge pockets and the vertical columns of the side frames, the resistance of the adapter side- frame interfaces against rotation, and the above-mentioned frictional resistance against relative movement between the transom-rocker seat interface, which as described above, depends upon the weight carried by the truck, and specifically the car body itself. However, with the advent of much lighter weight cars, as well as a need for lower height, or what are termed lower-deck, cars, the portion of the resistance to lozenging in the swing-motion truck attributable to the transom-rocker seat interface has been compromised by the very fact that these cars are of lighter weight. Thus, after considerable wear and tear, and when the trucks are being operated at high speeds, the tendency to lozenging is an ever-present possibility, which would not only lead to unstable primary or car body hunting, but also pose a considerable hazard of secondary or truck hunting which would occur at high speeds resulting in excessive forces on wheel and axles and truck and car body. Thus, in summary, the trend toward lighter weight and low-deck car bodies tends to diminish the operating efficiencies of the conventional swing-motion truck.
It is the objective of the present invention to overcome these deficiencies, and to ensure that lozenging of the truck proper does not occur during high-speed operations, which is achieved by rigidizing the truck to prevent parallelogramming, as well as to provide the highly-effective attributes of the swing motion truck for the prevention of uncontrolled resonance and primary or car body hunting, as well as to ensure that secondary or truck hunting is not experienced even at very high operating speeds.